a. Field of the Invention
This invention relates to voltage regulators and related control systems.
b. Related Art
A step-type voltage regulator is a device which is used to maintain a relatively constant voltage level in a power distribution system. Without such a regulator, the voltage level of the power distribution system could fluctuate significantly and cause damage to electrically powered equipment.
A step-type voltage regulator can be thought of as having two parts: a transformer assembly and a controller. A conventional step-type voltage regulator transformer assembly 102 and its associated controller 106 are shown in FIG. 1. The voltage regulator transformer assembly can be, for example, a Siemens JFR series. The windings and other internal components that form the transformer assembly 102 are mounted in an oil filled tank 108. A tap changing mechanism (not shown) is commonly sealed in a separate chamber in the tank 108.
The various electrical signals generated by the transformer are brought out to a terminal block 110 and external bushings S, SL, L for access. The terminal block is preferably covered with a waterproof housing. An indicator 112 is provided so that the position of the tap as well as its minimum and maximum positions can be readily determined.
A cabinet 114 is secured to the tank to mount and protect the voltage regulator controller 106. The cabinet 114 includes a door (not shown) and is sealed in a manner sufficient to protect the voltage regulator controller 106 from the elements. Signals carried between the transformer or tap changing mechanism and the voltage regulator controller 106 are carried via an external conduit 116.
The tap changing mechanism is controlled by the voltage regulator controller 106 based on the controller's program code and programmed configuration parameters. In operation, high voltage signals generated by the transformer assembly 102 are scaled down for reading by the controller 106. These signals are used by the controller 106 to make tap change control decisions in accordance with the configuration parameters and to provide indications of various conditions to an operator.
The transformer assembly 102 typically includes a switch or counter which changes state each time a tap change is made. This switch or counter is monitored by the controller 106 which, in turn, uses the signal generated by the switch or counter to keep track of the total number of tap changes made by the transformer. In order to ensure that the tap change or "operations" count is maintained in the event of a power loss, the controller may periodically store the count in a non-volatile memory such as an electrically erasable programmable read only memory (EEPROM).
One limitation of EEPROM technology is that it can only be written to a certain number of times before it wears out and the device fails. To avoid the wear out problem, a controller may store the operations count to EEPROM after a given number of tap changes (for example every 20 counts). A problem with this method is that an operations counter can suffer significant inaccuracies, especially for systems that lose power frequently.